Annunciators are electrical signaling devices, used in hotels or offices to indicate the sources of calls on a switchboard. It is an indicator that announces which electrical circuit has been active (as on a telephone switchboard). It annunciates the status of industrial processes, security and fire alarms of buildings. It may come in any combination of visual indication and/or audio alarms. A visual indication may be provided by a graphic display panel lit with lamps or bulbs, a digital display like that of an LED or LCD, or a computer or video monitor. These annunciators also include mosaic graphic displays, and control graphic displays. Audio alarm annunciators include air horns, sirens, bells, buzzers, speakers (for a paging system or voice evacuation), whoop sounders or hooters.